The present invention relates to an on-load tap changing apparatus of a transformer. More specifically, the present invention relates to a technique effective in being applied to the diagnosis of the degradation degree of insulating oil in a mechanical on-load tap changing apparatus.
An on-load tap changing apparatus is disposed in a transformer of an electric power transmission and distribution system. When the load of the electric power transmission and distribution system fluctuates and the change in voltage due to this fluctuation exceeds a fixed limit, the tap of the on-load tap changing apparatus disposed in the transformer is changed to keep the voltage of the electric power transmission and distribution system constant. The on-load tap changing apparatus includes a changing signal generation unit, an on-load tap changer, and an electrically driven operation mechanism, the on-load tap changer further including a changeover switching device and a tap selector (including a polarity changer or a transposition changer).
The outline of the changing operation of the on-load tap changing apparatus having such a configuration is as follows. That is, when the change in voltage exceeds the fixed limit, a signal is first created in the changing signal generation unit, so that the electrically driven operation mechanism is started to drive the on-load tap changer. As a result, the drive shaft of the on-load tap changer rotates, so that by the drive force of the drive shaft, the movable contact of the tap selector is disconnected and moved from one fixed contact, and is thrown into another fixed contact. In response to this, the changeover switching device performs the changing operation from one tap to another tap.
During the operation of the movable contact by the changeover switching device or at changing the tap of the tap selector, arc discharge occurs. This degrades insulating oil within the on-load tap changing apparatus, and in some cases, the internal device results in dielectric breakdown. On the other hand, likewise, discharge occurs in the tap selector and the polarity (transposition) changer.
In the conventional on-load tap changing apparatus configured as described above, in particular, when a fault is caused in the on-load tap changing apparatus of the electric power transmission and distribution system that serves as a main trunk line, the possibility of power failure over a wide range is high, which is a problem. Consequently, to prevent various faults, the maintaining and inspecting operation for the configuring devices and the configuring members is necessary. For this, the cover of the tap changing apparatus is opened periodically to evaluate the degradation degree of insulating oil by using oil extraction analysis by extracting the insulating oil. When the degradation degree progresses, the insulating oil is replaced.
As the diagnosing method for estimating the degradation degree and the life of insulating oil or insulating paper in an oil-immersed electric apparatus, a method by which, typically, furfural, carbon monoxide, carbon dioxide, and the like that are the decomposition products of the insulating paper are extracted from the insulating oil, and are subjected to gas analysis, thereby estimating the degradation degree from a separately determined correlation chart between the amount of gas generated and the polarization residual rate of the insulating paper, and the like are proposed. However, the above conventional technique is not a simple diagnosing method from the reasons of the request for special means that extracts, from the oil, a very small amount of gas generated with degradation, the large-sized evaluation apparatus for gas analysis, and the like.
As the background art of this technical field, for example, there is a technique as disclosed in Japanese Unexamined Patent Application Publication No. Hei10(1998)-74628. Japanese Unexamined Patent Application Publication No. Hei10(1998)-74628 discloses “A method by which a light source including at least two monochromatic light sources having wavelengths different from each other or a halogen lamp that emits white continuous light is provided, the irradiation light from the light source is spectrally dispersed through a spectroscope to at least two monochromatic lights having wavelengths different from each other, the at least two monochromatic irradiation lights that have been created in this manner are transmitted into an insulating medium, reflection light-absorption degrees (Aλ) at the respective wavelengths of the obtained lights are calculated, a reflection light-absorption degree difference (ΔAλ) or a reflection light-absorption degree ratio (Aλ′) between the two wavelengths is calculated, the relation (master curve) between the degradation degree of a material to be measured and the reflection light-absorption degree difference or the reflection light-absorption degree ratio is previously determined, and at measuring the degradation degree of the material to be measured, the obtained reflection lights are used to be subjected to comparison computation with the obtained master curve to determine the degradation degree.